dorsal/arxiv
View SchemaPhoto-Stimulated Electron Detrapping and the Two-State Model for Electron Transport in Nonpolar Liquids
| Authors | Ilya A. Shkrob, Myran. C. Sauer Jr |
|---|---|
| Categories | |
| ArXiv ID | physics/0411014 |
| URL | https://arxiv.org/abs/physics/0411014 |
| DOI | 10.1063/1.1871938 |
Abstract
In common nonpolar liquids, such as saturated hydrocarbons, a dynamic equilibrium between trapped (localized) and quasifree (extended) states has been postulated for the excess electron (the two-state model). Using time-resolved dc conductivity, the effect of 1064 nm laser photoexcitation of trapped electrons on the charge transport has been observed in liquid n-hexane and methylcyclohexane. The light promotes the electron from the trap into the conduction band of the liquid, instantaneously increasing the conductivity by orders of magnitude. From the analysis of the two-pulse, two-color photoconductivity data, the residence time of the electrons in traps has been estimated as ca. 8.4 ps for n-hexane and ca. 13 ps for methylcyclohexane (at 295 K). The rate of detrapping decreases at lower temperature with an activation energy of ca. 200 meV (280-320 K); the lifetime-mobility product for quasifree electrons scales linearly with the temperature. We suggest that the properties of trapped electrons in hydrocarbon liquids can be well accounted for using the simple electron bubble (Wigner-Seiz spherical well) model. The estimated localization time of the quasifree electron is 20-50 fs; both time estimates are in good agreement with the "quasiballistic" model. This localization time is significantly lower than the value of ca. 300 fs obtained using time-domain terahertz (THz) spectroscopy for the same system [E. Knoesel et al., J. Chem. Phys. 121, 394 (2004)]. We suggest that the THz signal originates from the oscillations of electron bubbles rather than the free-electron plasma; vibrations of these bubbles may be responsible for the deviations from the Drude behavior observed below 0.4 THz. Various implications of these results are discussed.
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"abstract": "In common nonpolar liquids, such as saturated hydrocarbons, a dynamic\nequilibrium between trapped (localized) and quasifree (extended) states has\nbeen postulated for the excess electron (the two-state model). Using\ntime-resolved dc conductivity, the effect of 1064 nm laser photoexcitation of\ntrapped electrons on the charge transport has been observed in liquid n-hexane\nand methylcyclohexane. The light promotes the electron from the trap into the\nconduction band of the liquid, instantaneously increasing the conductivity by\norders of magnitude. From the analysis of the two-pulse, two-color\nphotoconductivity data, the residence time of the electrons in traps has been\nestimated as ca. 8.4 ps for n-hexane and ca. 13 ps for methylcyclohexane (at\n295 K). The rate of detrapping decreases at lower temperature with an\nactivation energy of ca. 200 meV (280-320 K); the lifetime-mobility product for\nquasifree electrons scales linearly with the temperature. We suggest that the\nproperties of trapped electrons in hydrocarbon liquids can be well accounted\nfor using the simple electron bubble (Wigner-Seiz spherical well) model. The\nestimated localization time of the quasifree electron is 20-50 fs; both time\nestimates are in good agreement with the \"quasiballistic\" model. This\nlocalization time is significantly lower than the value of ca. 300 fs obtained\nusing time-domain terahertz (THz) spectroscopy for the same system [E. Knoesel\net al., J. Chem. Phys. 121, 394 (2004)]. We suggest that the THz signal\noriginates from the oscillations of electron bubbles rather than the\nfree-electron plasma; vibrations of these bubbles may be responsible for the\ndeviations from the Drude behavior observed below 0.4 THz. Various implications\nof these results are discussed.",
"arxiv_id": "physics/0411014",
"authors": [
"Ilya A. Shkrob",
"Myran. C. Sauer Jr"
],
"categories": [
"physics.chem-ph"
],
"doi": "10.1063/1.1871938",
"title": "Photo-Stimulated Electron Detrapping and the Two-State Model for Electron Transport in Nonpolar Liquids",
"url": "https://arxiv.org/abs/physics/0411014"
},
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